This invention is related to optical guided-transmission devices, particularly for use in integrated optical systems. An integrated guide is obtained by creating, in a substrate with a refractive index of n.sub.0, a zone in which the refractive index is more than n.sub.0. Integrated optical devices offer many advantages over conventional optical systems; they require no alignment, are perfectly stable, take up less space, remove the problem of vibrations, and provide an opportunity of achieving ultimate performance, by enabling light to be guided throughout its path. It is useful to be able to switch rays from one guide to another, in order to guide optical rays along several paths. Hybrid junctions are sometimes constructed using the principle of the directional coupler. This is a selector device comprising two wave-guides, made from an electro-optical material, and separated by another material, with a lower refractive index than the electro-optical material, by a distance of a few micrometers, so that a beam can be transfered from one guide to another. The refractive index of the two guides is altered in the reverse direction by the effect of an electrical field, thereby altering the length of the coupling and consequently the fraction of light energy passing from the first guide to the second. Such structures require a very high degree of geometrical precision, since a large number of variables have a critical importance for the length of the coupling; the interguide distance, in particular, has to be very strictly respected.
The new guide-transmission device described herein comprises two monomodal optical wave-guides which converge in a node from which a third monomodal guide starts. The three branches form a Y shape. The first two branches act as hybrid optical junction inputs, and the third branch acts as the first output, the second output being an integral transmission path inside the surrounding material. Such a junction accordingly forms an extremely simple integrated optical circuit. It is used primarily, but not exclusively in optical interferometers, which contain a number of beam separators that can be provided by these hybrid junctions. They may also contain phase modulators, which can be incorporated in the same circuits as the junctions.